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Prove the associative law of addition for real numbers. Output:
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Let a, b and c be real numbers.

(a + b) + c = a + (b + c) 

We will prove this using mathematical induction.

Base Case:

When n = 2, (a + b) + c = a + (b + c)

Let (a + b) = x ⇒ a + b + c = x + c ⇒ (a + b) + c = a + (b + c) 

Inductive Step:

Assume that (a + b) + c = a + (b + c) for n = k, where k ≥ 2.

Let (a + b) = x ⇒ a + b + c = x + c 

Let (x + c) = y ⇒ (a + b) + c = y 

Similarly, a + (b + c) = y  ⇒ (a + b) + c = a + (b + c)

Therefore, for all real numbers a, b and c, (a + b) + c = a + (b + c).